Vapor/thermal method of delaminating and stabilizing a phyllosilate and product

ABSTRACT

A method of delaminating a phyllosilicate is disclosed wherein the phyllosilicate is heated in the presence of a reactive vapor phase, preferably a hydrogen-containing atmosphere. The delaminated phyllosilicate is less than 1000 ANGSTROM  thick, and is stabilized against moisture pickup. The formation of either a layer of a transition metal, or an organic reactive site, on the phyllosilicate surface is also disclosed.

RELATED APPLICATION

An application filed of even date herewith in my name, now U.S. Pat. No.4,772,577 and entitled "Metal Coated Phyllosilicate and Method,"describes and claims a delaminated phyllosilicate particle having acoating of metal on its surface. Also disclosed and claimed are methodsof producing such metal-coated particles, and a ceramic-metal compositecomposed of such particles compressed into a solid body.

INTRODUCTION

This invention is concerned with providing a delaminated phyllosilicatethat is hydrolytically and hygroscopically stabilized, and with a methodof producing such material. Phyllosilicates are also known as hydratedsheet, or lattice layered, silicates.

The invention comprehends the entire genus of hydrated, or hydratable,phyllosilicates. It is especially concerned with the three layer micas,whether of natural or synthetic origin, although not so limited. Thesesilicate minerals include vermiculite, beidellite, nontronite,volchonskoite, saponite, stevensite, sauconite, pimelite, bentonite,montmorillonite, hectorite, the smectites, attapulgite, sepiolite,phlogopite, and biopyribole. The most widely known and extensivelystudied of these minerals, vermiculite, is of particular interest.

The silicate layer units in these minerals have a thickness of about 10Angstrom (Å) units, with the main elemental constituents being Mg, Al,Si, and O. These layers are separated by an interlayer composed of watermolecules associated with cations, such as Mg⁺⁺, Ca⁺⁺, Na⁺, K⁺, and H⁺.Before utilizing these minerals, it is frequently desirable todelaminate the particles, that is, separate the crystals at theinterlayer to form smaller particles.

It is conventional practice to delaminate the layered silicates byheating to an elevated temperature. This causes the water-containinginterlayer to expand and pop open. It has also been proposed to expandvermiculite particles by refluxing in an aqueous solution of a salt suchas lithium chloride. Subsequent application of a shearing force causesthe crystals to separate at the interlayer and form an aqueous gel.

My U.S. Pat. No. 4,676,929 describes a method of delamination wherein ahydrated phyllosilicate is dispersed in an expanding agent, which may bea primary aminocarboxy acid, or lysine orotate, or glycylglycine. Whenaccompanied by a shearing force, the expanding agent is effective, atambient temperature, to separate the silicate layer units of thephyllosilicate crystal in a matter of minutes, and form a gel.

RELATED LITERATURE

In addition to the patent just mentioned, and literature cited therein,reference is also made to my copending applications, Ser. No. 861,939and Ser. No. 862,256, both filed May 12, 1986. The former describessubjecting a phyllosilicate to an ion exchange treatment before reactingit with an expanding agent, as in U.S. Pat. No. 4,676,929. The latterdescribes subjecting a phyllosilicate to an ion exchange treatment, plusa thermal treatment, to develop a new crystal phase which forms a solidsolution.

Attention is also directed to the following U.S. patents:

U.S. Pat. No. 4,521,182 (Collins) discloses heating a particulatematerial, such as vermiculite, perlite, or clay, by directing a flamedownwardly within a vertical furnace, introducing the particulatematerial radially around the flame, and directing the material withinthe flame as it passes downwardly.

U.S. Pat. No. 4,539,046 (McAloon) discloses producing vermiculiteproducts that are stable in water by incorporating a source of ammoniain an aqueous suspension of vermiculite lamellae, shaping thesuspension, and removing water from the suspension by heating the shapedsuspension at a temperature above 100° C. The ammonia contacts thesuspension as the suspension is dried.

PURPOSES OF THE INVENTION

Phyllosilicates, as heretofore delaminated, have proven effective forsome purposes. However, in other instances, such as electricalapplications, the physical properties of the material have beeninadequate. It is a basic purpose of the invention to providedelaminated phyllosilicates having improved physical properties.

Another purpose is to provide a novel delamination method that providessuch improved properties.

A particularly troublesome problem, heretofore encountered withdelaminated phyllosilicates, derives from their hygroscopic nature. Aphyllosilicate is substantially dehydrated during delamination by heattreatment. However, there is a tendency to rehydrate once the materialis cooled and allowed to stand in air. A particular purpose of theinvention is to provide a delaminated phyllosilicate that is stabilizedagainst rehydration.

A further purpose is to provide a method of delamination capable ofproducing very finely delaminated particles.

A still further purpose is to provide a delaminated product havingreactive organic sites on its surfaces. Such sites may permitpolymerization and cross-linking to provide a uniformlychemically-bonded, ceramic-organic composite.

Another purpose is to provide a delaminated phyllosilicate wherein thedelaminated particles have a metallic film, or layer, on the particlesurfaces.

SUMMARY OF THE INVENTION

In furtherance of these purposes, and others that will become apparent,one aspect of the invention is a method of producing a delaminatedphyllosilicate that is hydrolytically and hygroscopically stabilized byheating the phyllosilicate in contact with a reactive, non-oxidizingvapor phase, for a time and at a temperature sufficient to causedelamination of the material. Preferably, the vapor phase is hydrogen,in an atmosphere of forming gas.

In one particular embodiment of the invention, the phyllosilicate may besubjected to an ion exchange with a metal ion prior to heat treatment inthe reactive vapor phase. In that case, vapor phase delaminatedphyllosilicate particles may have a metal film or coating formed ontheir surfaces.

In another embodiment, the phyllosilicate is heated in a selected vaporphase to produce controlled organic reactive sites, such as attachedradicals, pendent groups, or monomers, chemically bonded to thephyllosilicate surface.

The invention further resides in delaminated phyllosilicate particlesthat are less than 1000 Å in thickness, and that are hydrolytically andhygroscopically stabilized. In one specific embodiment, the particleshave controlled organic reactive sites, such as attached radicals,pendent groups, or monomers, chemically bonded to their surfaces. Inanother embodiment, the particles have a metal film formed in situ ontheir surfaces.

GENERAL DESCRIPTION OF THE INVENTION

The basic inventive method derives from my discovery that theundesirable tendency of a thermally delaminated phyllosilicate torehydrate can be greatly minimized, and a substantially stable materialprovided. I have found that, if the delaminating heat treatment isconducted in a controlled non-oxidizing atmosphere, this desirableeffect can be achieved. The atmosphere may be neutral or reducing, butmust contain, or be constituted by, a reactive vapor phase which may beH₂, CO₂, CO, NH₃, CH₄, or C₂ H₆, among others.

The delaminating heat treatment, in a controlled atmosphere, is asignificant change from previously practiced thermal delamination. Undersome circumstances, it may be effective at lower temperatures thanheretofore considered feasible. Also, as explained later, a higherdegree of delamination, even down to unit cell size, may be achieved.

Thus, a phyllosilicate, to be delaminated, may be heated to atemperature of at least about 400° C., but not over about 1000° C., fora period of time not exceeding about one hour. Longer times and/orhigher temperatures are generally unnecessary, but may be useful indevelopment of other properties. They tend to produce physical changesin the material, such as phase transitions, electronic and polychromaticproperties, or reduced surface area. For most purposes, optimumdelamination, with a minimum of side effects, such as reduced surfacearea, is achieved with heat treatment temperatures on the order of 800°C.

The heat treatment may be conducted in any chamber adapted tomaintenance of a controlled atmosphere. This may be either a batch typeunit, such as a batch kiln or closed vessel, or a continuous unit, suchas a tunnel kiln.

The unique feature is that the heat treatment is conducted in a neutralor a non-oxidizing atmosphere containing, or composed of, a reactivevapor phase. Where the sole concern is stabilization, forming gas oranhydrous ammonia is usually the preferred atmosphere. While hydrogenmight be used alone, forming gas is obviously much less expensive andsafer to use. Vapor phase materials, other than hydrogen, may beemployed, including carbon monoxide, carbon dioxide, methane, ethane,propane, methanol, and anhydrous ammonia. For special effects,especially formation of reactive organic sites on the delaminatedsurfaces, the vapor phase material may be anhydrous ammonia, or agaseous organic material, such as, ethylene oxide, methane, propane, orethane.

It is generally accepted that phyllosilicates, such as vermiculite, havean unbalanced negative ionic charge. It is my belief this is associatedwith --OH ions on the phyllosilicate surface, as well as with defects inthe crystal structure. I further believe that the effect of the vaporphase/thermal treatment of my invention is to remove such surface ions,and thereby satisfy the electronic charge. As a result, the neutralsurface is stabilized, or rendered functional, and resists moisturepickup after cooling.

My concept of the reactions occurring in the present method may bedepicted as follows:

1. H₂ O (molecular)+heat→H₂ O+partial delamination

2a. OH⁻ (structural)+H⁺ →H₂ O+further delamination+charge stabilization

or

2b. 2OH⁻ (structural)+2CO→2COOH→2CO+H₂ O+1/2O₂

I believe the presence of the reactive vapor phase not only exerts astabilizing influence, but tends to cause further delamination of thephyllosilicate. This is shown by the fact that the phyllosilicate may beso strongly delaminated that it is not visible to standard X-raydiffraction analyses. This means that delamination to at least less thana hundred unit cells (1000 Å) has occurred.

Electron microscope studies confirm that delamination to less than 1000Å has occurred. They further show that the particles are usually muchsmaller, even down to unit cell size in part. Thus, delaminatedparticles produced by vapor phase/thermal treatment are smaller thanthose obtained by prior techniques.

I believe this further delamination derives from removal of structuralhydroxyl ion (OH⁻) as illustrated in equation 2a or 2b above. This isalso thought to be a major factor in thermal delamination occurring atlower temperatures than previously deemed necessary.

However, if the phyllosilicate particles are compressed to form a body,such as a bar or disc, they tend to orient in layers or sheetsresembling the parent sheet structure. Such pressed bodies tend to showan apparent, or functional, aspect ratio of at least 100:1.

I have further found that phyllosilicate particles with metalliccoatings can be produced by providing the desired metal in, or on thesurface of, the particle prior to the thermal/vapor phase treatment. Thephyllosilicate may be heated in the presence of a metal compound toeffect anion exchange between the metal and ions from thephyllosilicate, such as Na⁺, K⁺, or Mg⁺⁺. Alternatively, the metalcompound may be dried on the surface of the phyllosilicate prior to thevapor phase treatment.

The ion exchange may also be effected by intimately mixing thephyllosilicate with a solution of a salt of the desired metal. For mostpurposes an aqueous solution is most convenient and economical to use.However, if desired, a non-aqueous solution may be employed, and may benecessary in some instances. Thus, a non-aqueous solution, such asalcohol, of aluminum chloride must be used in order to obtain analuminum, rather than aluminum oxide, coating.

X-ray diffraction (XRD) analyses show that ion-exchanged phyllosilicatesdelaminate at substantially lower temperatures than correspondingmaterials that have not been ion exchanged. This is especially true whenaqueous solutions of tin chloride (SnCl₂), antimony chloride (SbCl₃),lead acetate PbC₂ H₃ O₂, or copper chloride (CuCl₂) are employed tocarry out the ion exchange. For example, the presence of metallic tinwas observed by both XRD and DTA analyses on a sample delaminated byheat treatment at 400° C. in a forming gas atmosphere.

In many instances, only metals or metal oxides are revealed in an X-raytrace, even though chemical analyses have shown the metal component tobe less than 20% by weight. This further verifies that thephyllosilicate particles are less than 1000 Å in cross-section.

Infra-red analyses have shown that organic monomers can be chemicallybonded to the phyllosilicate platelet surfaces by proper selection ofthe vapor phase, as well as temperature. For example, with a methanevapor phase, the presence of methyl ions has been observed. Likewise,with a CO₂ phase, a carbonate phase has been observed.

There is a further reason to believe that a phyllosilicate surface,subjected to a reactive vapor phase, has been chemically functionalized.In many instances, surface area measurements, utilizing the N₂ -BETtechnique, are substantially lower than would normally be expected. Thisis believed to be due to interference by chemical groups during themeasurements.

Such reactive site formation does not occur under all conditions. Inparticular, lower temperatures on the order of 400°-500° C. appearfavorable. Frequently, it is desirable to delaminate at a highertemperature. In that event, the delaminated material may be cooledsubsequently to a predetermined intermediate temperature, and therequisite vapor phase introduced while the material is held at suchintermediate temperature.

SPECIFIC DESCRIPTION

By way of illustrating the improved stability achieved by the presentinventive method, several vermiculite samples from different sources, aswell as various other phyllosilicates, were subjected to comparativetests. Each sample was divided into four equal portions with eachportion being heated at 800° C. for one hour, but in a differentatmosphere. Thus, one sample was heated in air; a second in a carbondioxide atmosphere; a third in a forming gas (92% N₂ - 8% H₂)atmosphere; and the fourth in a methane atmosphere.

Subsequent to the heat treatment, each sample was observed to bedelaminated.

Each sample was weighed before and after its heat treatment to comparethe loss on ignition (LOI). Then, the samples were allowed to stand inair at a humidity level of about 40% and a temperature of 25° C. for 144hours to determine the per cent weight gain.

The materials tested were:

    ______________________________________                                               Material     Source                                                    ______________________________________                                        1.       Vermiculite    Eucatex brand                                         2.       Vermiculite    South Africa                                          3.       Vermiculite    North Carolina                                        4.       Vermiculite    Minebra brand                                         5.       Sepiolite                                                            6.       Bentonite                                                            7.       Kaolin                                                               8.       Talc                                                                 ______________________________________                                    

TABLE I tabulates the LOI values, and the % Wt. Gain values, observedfor each material, and each of the four treating atmospheres. Thematerials are designated by number as identified above.

                  TABLE I                                                         ______________________________________                                        LOI (%)             Wt. Gain (%)                                              Sample                                                                              Air    CO.sub.2                                                                             N.sub.2 /H.sub.2                                                                    CH.sub.4                                                                            Air  CO.sub.2                                                                           N.sub.2 /H.sub.2                                                                    CH.sub.4                      ______________________________________                                        1.    16.3   16.6   17.2  15.9  0.27 0.14  0.009                                                                              0.05                          2.    9.3    12.4   12.7   9.9  0.56 0.14 0.03  --                            3.    9.5    12.4   14.2  11.6  0.23 0.06 0.09  --                            4.    9.9    10.2   10.9  --    0.22 0.05 0.05  0.04                          5.    15.7   16.6   16.9  16.9  1.33 0.17 0.03  --                            6.    16.8   17.1   17.1  --    0.65 0.09 0.21  0.07                          7.    --     --     --    --    0.11 0.08 0.11  0.26                          8.    1.3     5.2    5.3   5.4  0.12 0.07 0.11  0.07                          ______________________________________                                    

It is evident that the firing in a reactive vapor phase is equally, ormore, effective in permitting volatile loss from the materials. However,the weight gain on standing is substantially less for the non-oxidizingvapor phase samples. The kaolin and talc samples are included asillustrative of natural materials frequently used as stable fillers inpaints, plastics, and gels.

The effectiveness of the invention was further illustrated by comparingthe volumes of four different gases evolved from treated and untreatedphyllosilicate materials. Samples of talc and vermiculite were eachdivided into two portions. One portion was retained in the "as received"condition, while the other was heated in a forming gas atmosphereovernite at 800° C.

The treated samples were cooled, and all samples were exposed to ambientatmosphere. Each of the four portions was then outgassed under vacuum ina mass spectrometer at several successively increased temperatures. Theamount of gas evolved from a sample was recorded at each temperature interms of four different gases evolved. The measured values werenormalized to microliters/gram for comparison.

TABLE II sets forth the normalized values at each temperature for eachof the four samples measured.

                  TABLE II                                                        ______________________________________                                        Temp. (°C.)                                                                       H.sub.2 H.sub.2 O N.sub.2 /CO                                                                           CO.sub.2                                 ______________________________________                                        Talc (as received)                                                            100        12      103       3       8                                        200        24      190       21      63                                       300        47      233       69      113                                      400        227     292       132     180                                      600        451     1496      165     340                                      800        1622    7874      347     128                                      1000       2076    2771      740     94                                       Total      4459    12,959    1477    926                                      Talc (treated)                                                                100        2       2         1       1                                        200        3       5         5       5                                        300        3       8         14      17                                       400        8       13        14      10                                       600        28      75        26      15                                       800        60      336       129     70                                       1000       79      326       224     96                                       Total      183     765       413     214                                      Vermiculite (as received)                                                     100        276     3160      40      50                                       200        178     2139      33      40                                       300        152     1908      42      54                                       400        173     1503      67      113                                      600        457     3950      388     1441                                     800        702     5067      342     232                                      1000       355     1272      371     384                                      Total      2293    18,999    1283    2314                                     Vermiculite (treated)                                                         100        1       8         1       3                                        200        2       18        2       7                                        300        5       21        9       18                                       400        13      36        11      18                                       600        43      233       13      9                                        800        349     1137      62      22                                       1000       672     1851      97      45                                       Total      1085    3304      195     122                                      ______________________________________                                    

The stabilizing effect is evident. Outgassing up to about 400° C. isconsidered to be primarily from the material surface. Above thattemperature, it is thought that internal, or structural, outgassingpredominates.

Electron diffraction studies were made on both vermiculite and talcsamples that had been thermally treated at 800° C. in a forming gasatmosphere. These were carried out since routine X-ray diffractionstudies did not show a 10 Å peak characteristic of the untreatedmaterials. The electron diffraction values observed were very close tostandard values for both materials as reported on JCPDS standard cards.However, lines below the 004 line, that is 001 and 002 lines, did notappear. This indicated that the materials were finely subdivided to lessthan a ten unit cell (100 Å) thickness, but that the original talc andvermiculite structures were retained.

The greater degree of delamination achieved in the presence of areactive vapor phase is further illustrated by transmission electronmicrographs (TEMs) taken of two talc samples and two vermiculitesamples. One talc sample was heated at 800° C. in air for one hour. Theother talc sample was heated in a forming gas atmosphere with the sametime-temperature cycle. Likewise, one vermiculite sample was heated at800° C. in air; the other in a forming gas atmosphere.

DESCRIPTION OF THE DRAWING

FIG. I is a TEM of the talc sample thermally treated in a forming gasatmosphere. The relative transparency of the particles indicated alayer, or C-axis, thickness of less than 1000 Å. Magnification was40,000×.

FIG. II is a TEM of the talc sample thermally treated in an airatmosphere. The total opacity indicates a much greater particlethickness than that of the FIG. I sample. Magnification was 20,000×.

FIG. III is a TEM of the vermiculite sample thermally treated in aforming gas atmosphere. The magnification was 253,000×, the micrographtransparency indicates the thickness less than 1000 Å, and the increasedmagnification shows the uneven particle surface. The latter is thoughtto arise from gas evolution from within the particle.

FIG. IV is a TEM of the vermiculite sample thermally treated in an airatmosphere. Magnification was 40,000×. As in the talc sample of FIG. II,the opacity indicates a much greater particle thickness than the forminggas treated sample of FIG. III.

I claim:
 1. A method of producing a delaminated phyllosilicate that ishydrolytically and hygroscopically stabilized by heating aphyllosilicate in contact with a reactive nonoxidizing vapor phase for atime and at a temperature sufficient to delaminate the phyllosilicate.2. A method in accordance with claim 1 wherein the time of treatmentdoes not exceed about one hour.
 3. A method in accordance with claim 1wherein the temperature at which the material is heated is in the rangeof about 400° C. to about 1000° C.
 4. A method in accordance with claim1 wherein the reactive vapor phase is hydrogen.
 5. A method inaccordance with claim 4 wherein the phyllosilicate is delaminated in aforming gas atmosphere.
 6. A method in accordance with claim 1 whereinthe phyllosilicate is vermiculite.
 7. A method in accordance with claim1 wherein the phyllosilicate is talc.
 8. A method in accordance withclaim 1 wherein the delaminated phyllosilicate is exposed to a selectedvapor phase at a temperature such that a controlled organic reactivesite is chemically bonded to the phyllosilicate surface.
 9. A method inaccordance with claim 8 wherein the phyllosilicate is delaminated at atemperature above that at which the reactive site forms, and thedelaminated phyllosilicate is cooled to an intermediate temperature forformation of the reactive site.
 10. A method in accordance with claim 8wherein the reactive site is an attached radical, a pendent group, or amonomer.
 11. A method in accordance with claim 8 wherein the atmosphereis carbon monoxide, and an organic monomer is formed on the surface. 12.A delaminated phyllosilicate composed of particles less than 1000 Å inthickness, and being hydrolytically and hygroscopically stabilized. 13.A delaminated phyllosilicate in accordance with claim 12 wherein thephyllosilicate surface has a reactive organic site attached thereto. 14.A compressed body composed of delaminated phyllosilicate particles thatare less than 1000 Å thick, are hydrolytically and hygroscopicallystabilized, and have a functional aspect ratio of at least 100:1.